Molecular weight regulation in polymerization of vinylidene monomers using isopulegol as regulator



United States Patent Richard E. Delacretaz, Speros P. Nemphos, andRobert ,7

L. Walter, Springfield, Mass., assignors to Monsanto Company, acorporation of Delaware No Drawing. Filed Nov. 3, 1961, Ser. No. 149,8713 Claims. (Ci. 26085.5)

This invention relates to the polymerization of a freeradical-polymerizable material including a polar monomer and moreparticularly relates to a method of regulating the molecular Weights ofpolymers prepared by polymerizing such a free radical-polymerizablematerial in the absence of an organic diluent.

The tendency of. certain free radical-polymerizable materials topolymerize to very high molecular weight polymers under normalpolymerization conditions is already well known. These very highmolecular Weight polymers have the disadvantage of being difiicultlyprocessable, i.e., unable to be processed without the use of specialprocessing equipment except at temperatures so high as to have adetrimental effect on the strength and color of the processed polymers.

Various techniques have been proposed for regulating the molecularweights of such polymers so as to make them more easily processable. Oneof these techniques is to conduct the polymerization in an organicdiluent. This technique is efiective as a means of lowering molecu-, larweight, but it has the disadvantages of increased cost and inconvenienceof separating the polymer from the organic diluent. Other proposedtechniques avoid the disadvantages of solvent polymerization but haveunfortunate disadvantages of their own, e.g., raising the polymerizationtemperature increases the danger of a runaway polymerization, and usinga mercaptan as a chain transfer agent contributes a very unpleasant odorto the polymers.

An object of the invention is to provide more easily processed polymersof the type prepared by polymerizing a free radical-polymerizablematerial including a polar monomer.

Another object is to provide a novel process for regulating themolecular weights of such polymers without employing an organic diluentin the polymerization reaction mixture.

These and other objects are attained by conducting the polymerization ofa free radical-polymerizable material including a polar monomer, ashereinafter more completely described, in the absence of an organicdiluent and in the presence of 0.2-5% of isopulegol, based on the weightof the free radical-polymerizable material.

The following examples are given to illustrate the invention. Unlessotherwise specified, quantities are mentioned on a weight basis, andpolymer properties are determined under the same conditions in each partof any one example.

EXAMPLE I Polyvinyl Chloride PART A Charge 100 parts of purified vinylchloride monomer, 150 parts of water, 0.15 part of lauroyl peroxide, and0.5 part of a water-soluble acrylic acid-Z-ethylhexyl acrylate (90:10)copolymer to a suitable reaction vessel. Seal the vessel and tumble itin a constant temperature bath at-50" C. for hours. The polymericproduct has a specific viscosity of 0.540, measured as a solution of0.25% of the polymer in cyclohexanone.

PART B Repeat Part A except for including 0.5 part of iso- 3,160,616Patented Dec. 8, 1964 pulegol in the charge to the reaction vessel. Thepolymeric product has a specific viscosity of about 0.400.

EXAMPLE II Polyacrylonitrile PART A Charge 100 parts of purifiedacrylonitrile and 0.1 part of dicumyl peroxide to a suitable reactionvessel. Purge with nitrogen, seal the vessel, and heat at 130 C. for 4hours. Dissolve the reaction product in dimethylformamide andprecipitate it in methanol to isolate methanolinsolubles. Themethanol-insoluble portion of the polymeric product has a specificviscosity of 0.447, measured as a solution of 0.1% of the polymerindimethylformamide.

. PART B Repeat Part except for including 1 part of isopulegol in thecharge to the reaction vessel. The methanolinsoluble portion of thepolymeric product has a specific viscosity of about 0.350.

7 EXAMPLE III Styrene-Acrylonitrile Copolymer PART A Charge a solutionof 2 parts of sodium stearate in 150 parts of water to a suitablereaction vessel and heat to 95-100" C. with agitation. Continuously adda mixture of parts of styrene and 20 parts of acrylonitrile to theheated, agitated soap solution over a period of 2 hours. During theaddition of the monomer mixture, continuously add a separate chargeconsisting of a solution of 0.25 part of potassium persulfate in 50parts of water. After completing the addition of the monomer andcatalyst charges, strip the emulsion of unreacted monomers, coagulate,and dry. The polymeric product has a specific viscosity of 0.180(measured as a solution of 0.1% of the polymer in dimethylformamide)PART B Repeat Part A except for adding 2 parts of isopulegol togetherwith the monomer charge. The product has a specific viscosity of 0.126.

The invention is a method of regulating the molecular weights ofpolymers prepared from a free radical-polymerizable material including apolar monomer without employing an organic diluent. The molecular weightregulation is achieved by conducting the polymerization of the freeradical-polymerizable material in the presence of a minor amount ofisopulegol.

The amount of molecular weight regulator employed in the practice ofthe'invention is in the range of 0.25%, usually 0.53%, based on theweight of the free radicalpolymerizable material. Isopulegol isinefiective as a molecular weight regulator at concentrations lower than0.2%. Concentrations higher than 5% are usually undesirable, eitherbecause the higher concentration causes too great a reduction of themolecular weight of the polymer or because the amount of molecularweight regulator which becomes chemically-combined into the polymer islarge enough to noticeably afiect polymer properties other than theproperties attributable to molecular Weight. A particular advantage ofthe molecular weight regulator of the invention is its ability to act asa molecular weight regulator at such low concentrations thatsubstantially its only contribution to the properties of the polymersprepared in its presence is an improvement in processability.

The free radical-polymerizable materials which are polymerized in thepresence of the molecular weight regulator of the invention arematerials including a polar monomer, i.e., a monomer which has a dipolemoment of at least 1.0 Debye unit. Particularly suitable materials are:

(1) Polar vinylidene monomers, such as acrylonitrile, methacrylonitrile,vinyl chloride, an alkyl acrylate (e.g., methyl acrylate, ethylacrylate, butyl acrylate, 2-ethylheXyl acrylate, dodecyl acrylate,etc.), an alkyl methacrylate (e.g., methyl methacrylate, butylmethacrylate, etc.), and mixtures thereof,

2. Mixtures of such polar vinylidene monomers with copolymerizablemonomers, such as dialkyl maleates, dialkyl fumarates, acrylic acid,methacrylic acid, conjugated dienes (e.g., butadiene), monovinylidenearomatic hydrocarbons (e.g., styrene, alpha-methylstyrene,alpha-ethylstyrene, m-, and p-methylstyrenes, 0-, m-, andpmethyl-alpha-methylstyrenes, p-isopropylstyrene, ar-dibutylstyrenes,vinyl naphthalene, etc.), and

(3) Mixtures of non-polar vinylidene monomers with one or morecopolymerizable polar compounds other than the polar monomers mentionedabove, such as monoor dialkyl maleates or fumarates, maleic anhydride,acrylic acid, methacrylic acid, etc.

A polar monomer should comprise at least of the weight of the freeradical-poly'merizable material. According to one of the preferredembodiments of the invention, the free radical-polymerizablematerialconsists of 10-90% by weight of one or more monovinylidenearomatic hydrocarbons and 90-10% by weight of acrylonitrile and/ ormethacrylonitrile.

The polymerization of the free radical-polymerizable material in thepresence of the molecular weight regulator of the invention is conductedin the absence of an organic diluent. Polymerization may be accomplishedby any of the mass, suspension, or emulsion polymerization techniquesconventionally employed for the polymerization of such materials,usually at temperatures in the range of -200 C. at atmospheric orsuperatmospheric pressure. The reaction mixture should contain a freeradical polymerization initiator, such as a peroxy or azo compound, andany ingredient required bythe particular polymerization techniqueemployed, e.g., water, an emulsifying agent, a suspending agent, etc.Optional ingredients, such as antioxidants, plasticizers, etc., can alsobe included in the reaction mixture if desired.

I A preferred embodiment of the invention is the use of the molecularweight regulator in polymerization reactions which are conducted in anaqueous medium. Ordinarily in such reactions the Weight ratio of waterto free radical-polymerizable material is in the range of 9:1 to 2:3.The emulsifying agent, when employed, can be of the anionic, cationic,or non-ionic type; the suspending agent, when employed, can be inorganicor organic.

It is within the scope of the invention to conduct the polymerization inthe presence of a preformed polymer, e.g., polybutadiene, a rubberybutadiene-styrene copolymer, or the like, to graft polymeric chains ofthe free radical-polymen'zable material onto the preformed polymerbackbone. The molecular weight regulator serves to shorten the chainsgrafted onto the polymer backbone as well as to lower the molecularweight of any co-formed, ungrafted polymer of the freeradicalpolymerizahle material.

The products of the invention are polymers which contain a minor amountof chemically-combined molecular weight regulator and have lowermolecular weights than the corresponding polymers prepared in theabsence of the molecular weight regulators. Because of their lowermolecular weights, they are more easily processable and can beprocessed, e.g., extruded, molded, etc., in conventional processingequipment without requiring the use of extreme temperatures which wouldhave a detrimental effect on the strength and color of the products.

The invention is particularly advantageous in that it accomplishesmolecular weight regulation without the aid of organic diluents,malodorous rnercaptans, or reactive materials which would have to beused in suchlarge amounts as to have a noticeable effect on otherpolymer properties as well as on processability.

It is obvious that many variations can be made in the products andprocesses set forth above without departing from the spirit and scope ofthis invention.

What is claimed is:

1. In a process for polymerizing a free radical-polymerizable materialofthe group consisting of (a) a polar vinylidene monomer of the groupconsisting of acrylonitrile, methacrylonitrile, vinyl chloride, an alkylacrylate, an alkyl methacrylate, and mixtures thereof, (b) mixtures ofsaid polar vinylidene monomer with a copolyrnerizable monomer of thegroup consisting of a dialkyl maleate, a dialkyl fumarate, acrylic acid,methacrylic acid, a conjugated diene, a monovinylidene aromatichydrocarbon, and mixtures thereof, and ('0) mixtures of a non-polarvinylidene monomer with a copolymerizable polar monomer of the groupconsisting of a monoalkyl maleate, a mon'oalkyl fumarate, a dialkylmaleate, a dialkyl fumarate, maleic anhydride, acrylic acid, methacrylicacid, and mixtures thereof in the presence of a free radicalpolymerization initiator, the improvement which comprises conducting thepolymerization in the presence of 0.2-5% of isopulegol, based on theweight of the free radical-polymerizable material.

2. A process as in claim 1 wherein the free radicalpolymerizablematerial consists of 10-90% by weight of a monovinylidene aromatichydrocarbon and 10% by weight of acrylonitrile.

3. A process as in claiml wherein the polymerization is conducted in anaqueous medium.

References Cited in the file of this patent UNITED STATES PATENTS2,363,044 Clifford Nov. 21, 1944 2,556,488 Wakeford et al June 12, 19513,110,702 Delecretaz Nov. 12, 1963

1. IN A PROCESS FOR POLYMERIZAING A FREE RADICAL-POLYMERIZABLE MATERIALOF THE GROUP CONSISTING OF (A) A POLAR VINYLIDENE MONOMER OF THE GROUPCONSISTING OF ACRYLONITRILE, METHACRYLONITRILE, VINYL CHLORIDE, AN ALKYLACRYLATE, AN ALKYL METHACRYLATE, AND MIXTURES THEREOF, (B) MIXTURES OFSAID POLAR VINYLIDENE MONOMER WITH A COPOLYMERIZABLE MONOMER OF THEGROUP CONSISTING OF A DIALKYL MALEATE, A DIALKYL FUMARATE, ACRYLIC ACID,METHACRYLIC ACID, A CONJUGATED DIENE, A MONOVINYLIDENE AROMATICHYDROCARBON, AND MIXTURES THEREOF, AND (C) MIXTURES OF A NON-POLARVINYLIDENE MONOMER WITH A COPOLYMERIZABLE POLAR MONOMER OF THE GROUPCONSISTING OF A MONOALKYL MALEATE, A MONOALKYL FUMARATE, A DIALKYLMALEATE, A DIALKYL FUMARATE, MALEIC ANHYDRIDE, ACRYLIC ACID, METHACRYLICACID, AND MIXTURES THEREOF IN THE APRESENCE OF A FREE RADICALPOLYMERIZATION INITATOR, THE IMPROVEMENT WHICH COMPRISES CONDUCTING THEPOLYMERIZATION IN THE PRESENCE OF 0.2-5% OF ISOPULEGOL, BASED ON THEWEIGHT OF THE FREE RADICAL-POLYMERIZABLE MATERIAL.